Although I was taught to boil new potatoes, older spuds hold their shape (and stay relatively dry for mashing) when done in a steamer. Do all vegetables retain more vitamin C when cooked this way?I've had a few queries about steaming and its effect on vitamin C in veg. First, I'll deal with the question of potatoes. The tendency to keep their shape or explode depends on the spuds you use. If they're floury (fianna, romano, sante or golden wonder), the cells swell and separate when cooked, and the potato becomes fluffy. If waxy (anya, charlotte, pink fir apple, etc), the cells stick together. All-purpose spuds (maris piper, desirée, king edward) are somewhere in between.

On average, a 175g serving of new potatoes in their skins provides 26mg of vitamin C – or 26% of your daily ration, according to the Potato Council. But the more you delve, the more you realise what a minefield this is. For example, the vitamin C content of potatoes diminishes in autumn and winter. And do some types of spud have more than others?

Anyway, heat and water are the enemies of vitamin C in potatoes, as they are in all vegetables. Vitamin C is soluble in water, and too long an exposure to heat causes nutrients to vanish. Minimise the time, temperature and amount of water. A microwave is one of the best ways to do this because it needs minimal water and the cooking time is very short. If you're boiling, use as little water as possible, and cook for the least possible time. Steaming is great, yes, but steam in small batches to minimise cooking time. Oh, and always cook spuds in their skins – it helps minimise the loss of both vitamin C and other nutrients.

I'm finding it hard to get fresh kaffir lime leaves. I've tried both frozen and dried, but they have nowhere near the same flavour. Where can I get fresh leaves? Ideally, I'd love my own plant.Kaffir lime is used in cooking all around south-east Asia, though over there they use the fruit as well as its leaves. Some Waitrose and Sainsbury's stores sell them – check if your nearest branch is one of them. Failing that, Harvey Nichols and Selfridges food halls in London have them. Of course, Asian supermarkets are an obvious source. If you don't have one close by, try citruscentre.co.uk, which will send you leaves from plants they grow themselves (£5 for 10 leaves). As for having your own ready supply, the plants are relatively easy to grow indoors in a pot – plants4presents.co.uk sells 40-60cm specimens, or larger, from £25; Cross Common Nursery has them for £32.

How do you make that quince ratafia you were going on about the other week?It's not quince season until October or so; I based it on a recipe in Good Things, by the immortal Jane Grigson, though I've altered it somewhat, most notably in the amount of sugar (I find Grigson's proportions make it too sweet). Take two large or three medium quinces. Wash them and rub off any grey down. Grate coarsely (skin, core and all) and put in a glass jar. Add 250g caster sugar, the peel of a lemon, two star anise, ½ cinnamon stick, two cloves and a filigree of mace. Cover with darkish rum (Grigson uses brandy or vodka, but I think the flavour profile of rum suits the fruit better), leave for two to three months, then strain and bottle. You can drink it right away. Incidentally, I use the macerated quince to make tarts that have proved rather popular. The recipe? I think that's for another column…